Versatile TIM Solution with Chain Network Solder Composite

ABSTRACT A novel epoxy-based SAC solder paste TIM system has been developed with the use of non-volatile epoxy flux. Cu filler was added to the solder paste, with Cu volume % of metal ranged from 17 to 60 volume % of metal. Formation of semi-continuous high melting Cu chain network was achieved, with Cu particles bridged by the CuSn IMC. This chain network, at sufficient concentration, serves as skeleton and maintains the shape of the sandwiched solder paste layer, thus prevents further spread out at subsequent SMT reflow process, and also allowed formation of TIM joint even in the absence of solderable metallization on flip chip and packaging housing. This chain network hampered the flow of liquid solder, thus restrained the expansion of outgassing, and consequently resulted in low voiding. Existence of crevices was attributed to excessive oxide brought in by Cu particles, and appeared to increase with increasing Cu filler content. Presence of ductile solder within TIM joint promises high resistance against brittle cracking under stress. The Cu content could be further optimized between 17 and 33 volume % of metal to avoid flux bleeding and maintain good epoxy adhesion between TIM phase and parts. The 20°C thermal conductivity achieved was 6.1 W/mK, and could be up to about 13 W/mK with further epoxy flux optimization.

Solderability of Coloured Lead Free Solder Composite

Coloured solders offer wide range of possible application on top of conventional usage related to solder and soldering. Coloured solder can be produced by adding colour pigment into solder formulation to form coloured solder composite. The performance of coloured solder joint typically determined by good solderability, which influenced by wetting properties. The objectives of this paper is to investigate the solderability of coloured lead free solder composite with different formulation type of colour pigment and variation of colour pigment composition. Green and “glow in the dark pigment” with composition of 5% and 10% respectively were added into the lead free solder paste. Each coloured solder paste was stencil printed on the PCB and then reflowed using reflow soldering process. The wettability of the solder composite was measured and observed using Infinite Focus Measurements (IFM). The results demonstrated that coloured lead free solder composite have a good wettability. This finding also indicates that use of green pigment into the solder composite has shown greater wettability as compared to glow in the dark pigment. Higher percentage of added colour pigment of 10% has significantly reduced the wettability of solder composite. Wettability of coloured solder composite with small amount of added pigment is in the acceptable range of contact angle, showing good solderability of joining.

Effect of TiO2 Reinforcement on Microstructure and Microhardness of Low-Silver SAC107 Lead-Free Solder Composite Solder

This research has investigated the physical performances of low-silver Sn-Ag-Cu (SAC) lead-free composite solder reinforced with titanium dioxide (TiO2). The SAC/TiO2 composite solder were fabricated via powder metallurgy (PM) technique. The five different composition chosen were 0, 0.25, 0.5, 0.75, and 1.0. The results showed that distribution of TiO2 along the grain boundaries has increased the hardness of the SAC/TiO2 composite solders compared to monolithic SAC solder alloy.

Development of Low Cost Sn-0.7Cu Base Composite Solder for High Temperature Application

This research has investigated the advantages of Sn-0.7Cu composite solder compared to conventional Sn-0.7Cu solder. The method used for fabricating the composite solder is a powder metallurgy (PM) technique. SiC and Al particles were added to Sn-0.7Cu powder during the mixing process. The Sn-0.7Cu solder composite that reinforced with 0.25 wt% of SiC and 0.5 wt% of Al, were successfully synthesized via PM technique. The result showed that the addition of SiC and Al were improving the mechanical properties and thermal stability of the solder as well as reduces the material cost.

Intermetallic Compound Formation on Solder Alloy/Cu-Substrate Interface Using Lead-Free Sn-0.7Cu/Recycled-Aluminum Composite Solder

Feasibility of using recycled-Aluminum (re-Al) as reinforcement particulates in Sn-0.7Cu is assessed by powder technology method, whereby re-Al particulates are produced from discarded aluminum beverage cans. This paper focuses on the intermetallic compound (IMC) formation study between the fabricated solder composite on Cu-substrate. Throughout this study, four different composition of Sn-0.7Cu/re-Al (0.0, 3.0, 3.5, 4.0 wt.%) were studied. X-ray diffraction (XRD) was used to analyze the IMCs phase formation between the interfaces. New IMC phase of Cu9Al4was detected beside Cu6Sn5and Cu3Sn in the composite solder samples. However, Sn-0.7Cu/3.0re-Al showed least formation of brittle IMCs compared to the monolithic solder.